A parking brake actuating assembly is typically installed in a passenger compartment of a motor vehicle adjacent the driver's seat. The motor vehicle has a brake system that is actuated to prevent vehicle wheel rotation and hence rolling movement of the vehicle by applying tension to a vehicle brake cable that connects to the brake system.
The typical parking brake actuating assembly comprises a stationary sector having a plurality of teeth. A brake lever is mounted for pivotal movement relative to the sector and is adapted to be operatively connected to the vehicle brake cable. The brake lever is pivotable in a brake applying direction to a braking position to apply tension to the vehicle brake cable and in a brake releasing direction opposite the brake applying direction to a released position to release tension on the brake cable and release the vehicle brakes. A pawl is normally mounted to the brake lever for movement between engaged and disengaged positions relative to the sector teeth. When the pawl is in the engaged position and the brake lever is in the braking position, the pawl engages the teeth to prevent the brake lever from pivoting in the brake releasing direction. When pawl is in the disengaged position, the pawl disengages from the teeth to allow the brake lever to pivot from the braking position thereof towards and into the released position thereof. An elongated release member is mounted to the brake lever for longitudinal movement relative to the brake lever between normal and depressed positions. An activation button, which protrudes out of an outer end of the brake lever, is connected to an outer end of the release member. An inner end of the release member is connected to the pawl such that when the release member is moved into the depressed position, the pawl is forced into the disengaged position.
In this type of brake actuator assembly, the tension created in the brake cable system when the lever is in the brake applied position tends to force the pawl into a binding engagement with the sector teeth. To move the lever to its brake released position, the user first lifts the brake lever slightly in the brake applying direction to remove the cable tension load from the pawl and then depresses the activation button to disengage the pawl. It is possible for the brake lever to be released unintentionally if an impact force is applied to the button with a high enough force to overcome binding engagement created between the pawl and the sector teeth by the cable tension load. It is desirable to prevent the parking brake actuator from being unintentionally released by such an impact force.
U.S. Pat. No. 4,881,425 (hereinafter “the '425 patent”) discloses a parking brake actuator designed to reduce the chances of such an unintentional release of the parking brake by positioning a motion-absorbing spring within the activation button in engagement with the end of the release member. When a user depresses the activation button, the spring compresses and transfers its stored energy to the release member, which urges the release member into its depressed position, in turn urging the pawl into its disengaged position. When the parking brake is in its brake applied position with the cable tension load binding the pawl with the sector teeth, depressing the activation button without lifting the lever in the brake applying direction simply compresses the spring without disengaging the pawl from the sector teeth. That is, the spring is sufficiently weak to allow the button to be depressed without overcoming the binding of the pawl with the sector teeth and moving the same into its disengaged position. If a user wishes to release the parking brake he must first lift the brake lever slightly, thereby reducing the cable tension load on the pawl and then depress the activation button to move the pawl into its disengaged position. Because it is unlikely that a user will unintentionally depress the activation button and rotate the brake lever in the brake applying direction, the likelihood of an unintended release of the parking brake is reduced.
The parking brake actuator disclosed in the '425 patent has several shortcomings. The spring disposed between the activation button and the release member is disposed at a narrow outer handle of the brake lever, which is designed to permit a user to wrap his hand around the brake lever. The required incorporation of the spring into such a small area complicates the manufacturing process because the spring must be coiled, inserted, and held in a very small space during assembly. It is also difficult to manufacture the small but intricate activation button.
Japanese Utility Model Laid-Open Publication No. JP357186562A discloses another parking brake actuator that reduces the likelihood of an erroneous release of the parking brake and operates in a similar manner as the actuator of the '425 patent. However, instead of using a motion-absorbing spring disposed between the activation button and the release member to provide the urging force, the actuator disclosed in the Japanese Publication utilizes a single flexible release member that elastically deforms to absorb the motion of the activation button when depressed. An available commercial version of the design disclosed in this Japanese application uses a flexible plastic rod for the release member. This brake actuator also suffers from a major shortcoming. Because the disclosed release member is constructed from a flexible material, the resulting release member tends to fatigue faster than would be the case with a rigid release member.
Consequently, there exists a need in the art for a parking brake actuator with an anti-release feature that eliminates the difficulties encountered by the above-described conventional devices.